Theoretical Study Of Photoelectons' Ultrafast Dynamics In Intense Laser Pulses

With the development of laser technology,the interaction of atoms,molecules and condensed matter with ultraintense and ultrafast laser pulses bring many new physical phenomena.The study of strong laser physics provides a powerful technology on the measurement and control of ultrafast dynamics in material,which is of great scientific significance and application value.This thesis develops classical trajectory Monte Carlo method and de Broglie-Bohm Method,combined with numerical solution of timedependent Schroedinger equation,and performs a deep investigation on electrons' ultrafast dynamics in the Coulomb potential and the periodical potential.The main content consist of three parts:In the first part,we studied the connection among three near-threshold processes:Teraherz wave generation,low-energe photoelectons and Rydberg states electrons.Using three-dimensional classical trajectory Monte Carlo method,the maps of electrons' final energy on tunneling coordinates in linearly polarized two-colored laser field and few-cycle laser field are presented respectively.The Coulomb potential plays an important role in all those three near-threshold processes.In analysis of modulation behaviors of electrons' spectra with the asymmetry of laser field,the Terahertz wave generation is mainly contributed by the forward scattering electrons,which is the same as the low-energy electrons,While the Rydberg state electrons' generation shows a opposite modulation behavior with them.The connection among Teraherz wave generation,low-energe photoelectons and Rydberg states electrons are built in a unified physical picture,which establishes a theoretical foundation of the synchronizing Terahertz wave and photoelectron measurements.In the second part,we studied the all-optical attoclock technology based on the measurement of Terahertz waves' polarization directions.The photoelectron spectra and photocurrents in circularly polarized few-cycle laser pulses are calculated and their offset angles are found to be the same.Due to the effects of the ground state depletion and the Coulomb potential,the offset angles as a function of laser intensity shows a knee structure.This structure exists universally in the interaction between different wavelength laser and different kinds of atoms.Using the Terahertz wave Air-Biased-Coherent-Detection(THz-ABCD)technology,we measure the Terahertz wave generated in the interaction between circularly polarized 800 nm laser pulse + linearly polarized 400 nm laser pulse and inert gas targets.The polarization directions of terahertz wave are found to rotate with the phase delay between these two-colored pulses.The measured polarization directions as a function of laser intensity shows a knee structure too,which suggests that the alloptical attoclock technology based on the measurement of Terahertz waves' polarization directions can perform the same measurement as the traditional attoclock.In the third part,we studied the high-order harmonics generation in solid and radiation of tunneling wavepacket.We introduced the quantum trajectory concept into the high-order harmonics generation in solid for the first time.Using the de Broglie-Bohm Method,electrons' dynamics in the periodic potential are investigated.Due to the nonlocal property of the quantum wavepacket,different quantum trajectories show similar dynamical Bloch oscillation behaviors,while their harmonics spectra are very different.With the increase of the laser intensity,frequencies of dynamical Bloch oscillations are raised and all trajectories' entire movement with the laser field could appear.In the study on the radiation of tunneling electron's wavepakcet are investigated for the first time.Without electrical field,two radiation generation moments appear on the ascending side and the descending side with the increase of wavepacket's initial energy.Deduction of time and space information using the tunneling radiation provide a new path of all-optical attoclock.Under the static electrical field,reflected wavepackets are accelerated back to the barrier and the interference of electron's wavepacket appears with complex radiation structures.